In the field of material process machinery, there are many situations where it is desired to maintain the tension on a continuum of moving material. Thus, for example, in the field of metal wire drawing, it is known to cause wire drawing stock coming from a supply reel to pass through a "dancer" into a wire drawing machine. The dancer, which is a tensioning device, may consist of a pair of sheaves, or pulleys, mounted on axles at the top of a support frame, with a third pulley, optionally weighted and/or spring loaded, positioned therebetween and within guide-tracks. Since the center pulley is free to move up and down in the tracks, the filament of wire may be caused to ride over the tops of the first and second pulleys, and under the middle one, so that the inherent bias of the latter is free to work in opposition to tension variations on the wire. As tension on the wire is increased, the center pulley will move upward in its tracks in response until the point when the tension and the counter-force exerted by the dancer are equal, at which point the upward travel of the center pulley will cease. Until those forces are equalized, the center pulley will continue to travel upward. Thus, the length of the tracks must be sufficient to accomodate the time over which the increased tension occurs, otherwise the tension on the wire will increase sharply when the center pulley reaches the end of its permissable travel at the top of the tracks. Further, through operation of Newton's Third Law, as tension is applied to the wire, the weight and/or spring bias of the central pulley causes the wire to "see" a transient increase in tension as an equal and opposite reaction until the pulley is traveling upward at a velocity sufficient to offset substantially the transient constituent of the increase in tension. Although the wire may be more or less ductile, and some "necking down" may occur as a result, it normally is insignificant in amount, and of no appreciable consequence anyway in view of the ensuing operations (e.g., wire drawing) to which the wire is subjected. Similarly, when the material in process is thread or yarn, substantially the same considerations obtain, so such dancer-type tension devices have also been found to be satisfactory in such applications.
Other tension devices operate on the principle of beam deflection, as by mounting a tension pulley at the end of a wand or beam, and/or on the principle of spring loading with or without weight or beam deflection augmentation. Although with such alternative devices, singly or in combination, the configuration of loading on the continuum of material being processed in response to it being tensioned may be varied, they may also exhibit equal and opposite reaction phenomena of the type experienced with "dancers". Further, such devices typically have a more limited travel displacement path than dancer-type tensioners, and also may have the adverse characteristic of non-linear tension increases as a function of the displacement of the pulley.
Again, such characteristics are tolerable with a number of materials, such as some metal wires or textile yarns, and so, as a practical matter, are acceptable for a wide variety of uses. However, there are a number of applications where it is necessary or desirable to accomodate processing variations without introducing significant tension variations to the material being processed, because the material itself is not capable of tolerating such tensioning. Such materials include those with a low breaking strength, those which are so ductile as to be susceptible to permanent, objectionable, cross-sectional distortion, and those which, although recoverable from tension introduced size and/or dimensional variations when the increased tension is removed, are likely to exhibit objectionable tension induced distortions at a critical stage in processing. Thus, for example, in the field of tire making, the bead wires which form the reinforcement for the tire edges that are juxtaposed to the wheel, are wrapped with so-called "chafing strips" at an early stage in the process of manufacture of a tire. These strips, made from ribbons of unvulcanized rubber, and typically about 2 inches wide and about 1/64 to 1/32 inch thick, are subject to stretching under relatively light tension, with consequent radical narrowing and reductions in thickness of the material. Friction variations in a pay-off mechanism, differing rates of take-up, and changes in the size and/or contour of the surfaces to which the material is being applied, for example, may introduce changes which, if a tensioning device were used, would result in variations in tension on the material being processed. As a result, if application and tension occur simultaneously, significant portions of the tapes may not abutt or overlap, or they may produce overlay thicknesses which are not uniform or according to acceptable design limitations.
Accordingly, it is an object of this invention to provide means for stabilizing, within acceptable limits, the configuration of elongated materials in process without significant changes in the tension thereof.
Another object of this invention is to provide such means to so stabilize such material substantially throughout the entire time period over which processing variations occur.
Yet another object of this invention is to provide means for satisfying the foregoing objectives to accomodate materials which are susceptible to significant "necking-down", thickness reductions and/or other cross-sectional distortions while under the influence of variations normally encountered in process.
Still another object of this invention is to provide means for satisfying the foregoing objectives in which the stabilization characteristics may be varied finely over a range of setting.